The present invention relates to a rotary ball valve assembly and a method for forming such assembly efficiently and economically to provide a leak-proof assembly ready for installation in a fluid flow line. Rotary ball valves are frequently sold with short lengths of copper tubing brazed thereto which function as stubs suitable for brazing to a fluid flow line at the site where the valve is desire to be installed. The prior art rotary ball valve assemblies typically include a housing containing the rotary ball valve, seals and/or seats, one on each side of the ball, a spring urging the seals or seats into sealing engagement with the ball and a separately formed threaded collar threadedly engaged to the body and compressing the spring. Some prior art valves omit the spring and rely on the threaded collar to compress the seals and/or seats into sealing engagement with the ball.
One such type of prior art valve is manufactured by Aeroquip Corporation, the assignee of the present application, and sold under its Part No. RB01-004-141414. Such prior art rotary ball valve assemblies are provided with a stub at each of the inlet and outlet ends. One of such stubs is brazed to the collar which is threadedly engaged to the housing and the other stub is brazed to the housing itself. A type of spring frequently utilized to apply compressive loads within the assembly is a stainless steel wave spring formed from a single strip or length of metal having a wave pattern with alternating crests and grooves. The strip of metal is wound to form a coil in which the outer periphery of each of the plurality of individual coils generally define a cylinder of a size permitting the spring to be received in a cylindrical length of tubing. The strip is wound such that the grooves of any given coil or wave are each aligned with a crest of the adjacent coil and with a groove of the next alternate coil or wave. This alignment results in alternating contact points and gaps around the periphery of pairs of adjacent coils or waves.
In applying the threaded collar to the housing in prior art rotary ball valve assemblies, the collar directly contacts the spring prior to becoming fully engaged. Further rotation of such collar following its initial contact with the spring as it is rotated on the threads of the collar to its fully engaged, sealing position, places a torsional load on the spring. Such torsional load applied to the spring has a tendency to rotate coils or waves closest to the collar relatively to the coils or waves which are closer to the rotary ball valve with the result that the aligned grooves and crests of adjacent coils or waves may become dislocated from one another so that some of the crests of one coil will be aligned with crests of an adjacent coil. Such dislocation causes the spring to have less compressive force than intended when the aligned grooves and crests are fully in aligned contact with one another.